[Request for review] Profiling the FreeBSD kernel boot

blubee blubeeme gurenchan at gmail.com
Fri Dec 22 14:05:13 UTC 2017

On Fri, Dec 22, 2017 at 5:44 PM, Colin Percival <cperciva at tarsnap.com>

> Hi everyone,
> For the past few months I've been working on code for profiling the FreeBSD
> "kernel boot", i.e., everything between when kernel code starts running and
> when we first enter userland as init(8).  This is not trivial since it's
> impossible to use tools like dtrace to monitor things prior to when said
> tools are running.  The goal of this exercise is to help me track down the
> places where we're wasting time during the boot, and then to fix them.
> The approach I've taken is to add some macros -- most notably TSENTER() and
> TSEXIT() -- which by default compile to nothing, but if the TSLOG kernel
> option is enabled they compile to code which logs the cycle count (e.g., on
> x86 the value from the RDTSC instruction) along with some other data (in
> the
> case of TSENTER and TSEXIT, the fact that we're entering/exiting a
> function).
> This can then be dumped via a sysctl (debug.tslog) and processed in
> userland
> to convert function entries/exits into stacks and to visualize the time
> spent
> in the boot process.
> Two examples:
> A flame chart of my laptop booting HEAD:
> http://www.daemonology.net/timestamping/tslog-laptop.svg
> A flame chart of an EC2 c5.4xlarge instance booting 11.1-RELEASE:
> http://www.daemonology.net/timestamping/tslog-c5.4xlarge.svg
> The patches (10 of them, to be applied in order), userland scripts, and
> very
> brief usage instructions are at:
> http://www.daemonology.net/timestamping/tslog.tgz
> I hope to commit the patches in the next week, since I'm planning on
> writing
> a paper to submit to AsiaBSDCon (which has a deadline of December 31st); so
> if anyone has interest/time to look at this in the near future (I mean,
> it's
> not like anyone is going to be busy this weekend, right?) I'd love to have
> some feedback before it goes into the tree.
> --
> Colin Percival
> Security Officer Emeritus, FreeBSD | The power to serve
> Founder, Tarsnap | www.tarsnap.com | Online backups for the truly paranoid
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I've gotta say  nice work with the tracing.
Hopefully your talk gets accepted, i'd love to hear it.

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